Prestretching of wire ropes and the like



sepf. 1o, 1940.

WHW Will m, 'fsw illlllllllll [mele/02 E0/Vaga C Pf6/M4 Patented Sept.10,v 1940 UNITED STATES PRESTRETCHING F WIRE ROPES AND THE LIKE LeonardC. Peskin, Worcester, Mass., assignor to The American Steel and WireCompany of New Jersey, a corporation of New Jersey Application July 18,1939, Serial No. 285,221

9 Claims.

My invention relates to the prestretching of wire ropes or otherstructures formed of assembled wires or strands, for the purpose ofretarding or preventing the structure from unduly stretching when placedin service.

As a result of investigations into the Vibration fatigue characteristicsof various wire ropes, conductors, etc., I noticed the remarkableaccelerating effect the presence of vibration has on the `stretchingcharacteristics of such composite structures as ropes, conductors,cables, etc. Upon conceiving the possibilities of applying vibration tothe prestretching of ropes, etc., I conducted a series of tests on theeffects of applying various combinations of tensions and vibrationfrequencies to Wire center and hemp center'wire ropes. These few testsrevealed the following significant facts:

a. Vibration combined with tension can eiect a greater prestretching orconsolidation of the structure in a matter of minutes (10 or less) thantension alone can in many hours (24 or more).

b. 'I'he tension needed for eecting the prestretching under vibrationcan be considerably smaller than the tensions (50 per cent or more ofthe ultimate strength) commonly used for static stretching of likestructures.

c. Both increase in amplitude or frequency of vibration accelerate thestretching effect, the frequency being considerably more effective inits action than the amplitude.

d. The vibration stretching establishes a condition of equilibrium andstability in the roper against further stretching or creep due tomechanical set.

e. The modulus of elasticity of the rope or strand structure can beraised as much as 40 per cent by the vibration stretching treatment.

As a result of these few observations, I have developed certainworthwhile ideas with regard to the application of vibration stretching,as follows:

a. 'I'he prestretching oiv ropes has long been recognized as desirablefor stabilizing and balancing rope constructions, but the present staticmethods of loading individual lengths has necessitated using large loadsand considerable space for the equipment. As a result, very heavy andspacious equipment is used for the few ropes that are prestretched.Furthermore, the length of time involved in stretching by the staticmethod makes the treatment very costly. However, vibration applied tothe stretching operation makes it possible to greatly reduce both thetension and 4balancing the rope or strand structure. Furthermore, thelighter loads yand shorter time make it possible to apply the vibrationstretching treatment to long continuous lengths of rope either in 5 aseparate machine as a vseparate treatment. or continuously as the ropecomes from the stranding machine. The mechanism for providing thistreatment will be explained later.

b. By applying this vibration stretching-to ropes in general, I would bein a position to produce a rope having superior characteristics to thoseof ropes not prestretched. For one thing, I could largely remove thecreep characteristics of ropes commonly applied to elevators, shovels,etc. I also have reason to believe, from other tests I have made, thatthese prestretched ropes have superior impact or shock resisting abilityas compared to nonstretched ropes. Incidentally, tests show theseimprovements to persist even if the ropes are considerably handled afterbeing prestretched and before being lput into operation.

c. Perhaps the most immediate important application ofvibrationstretching is that of prestressing rural transmission lines.Three-wire conductors are of such an unbalanced construction thatvariations in modulus of elasticity can. be very pronounced. Also, thestretch characteristics of this type of conductor leave 'much to bedesired. 'By subjecting this conductor to 30 vibration stretching, I cannot onlyv establish a uniform modulus in the conductor, but I can alsostabilize it against further creep and thus do away with the. necessityof .resagging lines strung with this conductor.

d. Other important applications of the vibration stretching treatmentcan be made to such special cables as are used vfor oil well explorationand well shooting. Cables supplied for this purpose must now beprestretched by running them 40 either into old wells or pulling themwith trucks. 'I'hese cables are ver'y long, running from 10,000 tov15,000 feet. This vibration stretching treat-- ment can be continuouslyapplied to these cables in the manner to be described.

With respect to applying the vibration stretching treatment to ropes,cables, conductors, etc., the apparatus consists essentially of -a meansfor applying a controlled tension to every part of the structure beingtreated, and a means for simul- 50 taneously applying a controlledvibration to those parts being stretched.

An example of such apparatus is illustrated by the accompanying drawing,in which:

Figure 1 is an elevation;

Figure 2 is a plan;

Figure 3 is a plan of a modification; and f Figure 4 is -a diagram ofhow the vibration may be controlled;

The device for continuously applying tension to long lengths of rope,etc., can take a variety of forms. It may be either a separate machineor part of a stra-nding machine. Two schemes are shown on theaccompanying drawing. 'I'he rope I passes continuously from a set ofstationary haul-off sheaves 2 to a similar set 3 whose distance from therst set can be adjusted to any desired length.V Tension is applied tothe rope` through a hydraulic ram 4 linked by cable ties 5 to theadjustable position haul-0E 3. The pressure in the hydraulic ram 4 canbe adjustedv to give any desired tension on the moving cable. Thispressure is coupled through an elctric valve and relay to the haul-olfmotors 6 and 1 in such a manner as to maintain a difference in speed onthe two haul-ofi` motors which will automatically create the tension inthe rope originally set on the hydraulic ram '4. The arrangement isreversible so that the rope -can pass back and forth as many times asdesired.

In operation, the ram is adjusted to give a certain denite tension tothe rope. 'I'he span and haul-oit motor speeds are adjusted to give ashort or long time treatment to the rope. From that time on the electricvalve and relay would automatically control the difference in motorspeeds so as to maintain continuously the desired tension. Without suchtension controls the rope, etc., could be seriously overstressed whensubject to the diiferental haul-offspeeds if it happened to have a tightsection, and considerably understressed if ,the rope construction becamerelatively loose in another between the sheaves.

The haul-off sheaves and loading ram can be placed inline, as shown inFigure 1, or arranged as shown in the alternate Lvlayout of Figure 3, iffound more convenient. Other schemes for applying tension can be used,as .for eXtmple, pulling against dies or snubbing sheaves, etc. I n allcases a mechanism as described for controlling the tension is anecessary part of the equipmentto insure uniformity of product and avoidover-- stressing the structure; c

Without vibration the elementsof the rope structure can get intosuch.pos'itions that the mere application of tension will fail toproperly `consolidate the structure.

high frequency vibration causes the inertia of the individual wires andstrands to come into play, causing an internal manipulation, of the ropeso that under a relatively small tension the individual componentsquickly .fall into their most stable position. i

'Ihe vibration applied to the rope should be of suiicient amplitude andfrequency to call into play the inertia of the individual components.These amplitudes and frequencies will depend upon the structure beingtested, as well as the tension applied. Although lateral vibration ismost easily applied, the effect can be achieved by the use of torsionalvibration or longitudinal vibration, as well as any combination oflateral,

. torsional, and longitudinal vibration.

A number of means for applying vibration to a continuously moving rope,etc., under tension are possible, as for example: l a. A variable orfixed speed motor can be connected through a variable throw crank andsuitable pulley guides to the structure being tested,

part while passing The application of and the latter vibrated by forcedvibrations. Due to poor coupling conditions at forced vibration, thiswill require a motor of large horsepower.

b. A variable speed motor 8 can be made to vibrate the rope I, as shownin Figure 4, at any natural 'frequency of the rope by means of asuitable frequency pick-up 9 with a. lter and speed control I0. Atnatural frequency operation, a low horsepower motor is suflicient.

c. A special electromagnetic vibrator motor as used in certain vibrationfatigue equipment can be applied to the rope and the latter vibrated atany natural frequency. 'I'his motor acts magnetically like a loudspeaker in which the rope takes the place of the diaphragm. d.Alternating current can be passed through the rope while it passesbetween the poles of a D. C. magnet. The interaction of the magneticfields will cause the rope to vibrate.

e. Other means, electrical or mechanical, involving resonant or forcedvibration of the ro can be applied.

I claim:

1. A method of prestretching wire ropes or other structures formed ofassembled wires or strands, including vibrating successive lengths ofthe structure while it is under prestretching tension, the frequency atwhich the structure is vibrated being sufficiently high to imparta'sufficiently great force to the vibrating components of the structure.to cause these' components to adjust themselves to positions bestadapted to withstand the tension applied the structure when it is inservice.

2. A method of prestretching wire -ropes or other structures formed ofassembled wires or strands, including vibrating successive lengths ofthe structure while it is under prestretching tension, the frequency atwhich the structurel is vibrated being sufhciently high to impart asufficiently great force to the vibrating components of the structure tocause these components to adjust themselves to positions best adapted towithstand the tension applied the structure when it is in service, theprestretching tension used,-

being substantially less than is necessary when a similar structure isprestretched under static tension to accomplish comparable results.

' 3. A method of prestretching wire ropes or other structures formed ofassembled wires or` coiling and uncoiling so as to tension the struc- Iturein this span and vibrating the tensioned portion of the structure,the frequency at which the structure is vibrated being suiiiciently highto impart a sumciently great force to the vibrating components of thestructure to cause these components to adjust themselves to positionsbest adapted to withstand the tension applied l the structure when it isin service.

5. A method of prestretching wire ropesl or other structures formed ofassembled wires or strands, including coiling and uncoiling thestructure so as to provide a continuously moving span of the same,controlling the rate of the 75 coiling and uncoiling so as to tensionthe structure in this span and vibrating the tensioned portion of thestructure, the frequency at which the structure is vibrated beingsufficiently high to impart a sufficiently great force to the vibratingcomponents of the structure to cause these components to adjustthemselves to positions best adapted to withstand the tension appliedthe structure when it is in service, the prestretching tension usedbeing substantially less than is necessary when a similar structure isprestretched under static tension to accomplish comparable results. A

6. A method of prestretching wire ropes or other structures formed ofassembled wires or strands, including coiling and uncoiling thestructure so as to provide a continuously moving span of the same,controlling the rate of the coiling and uncoiling so as to tension thestructure in this span and vibrating the tensioned portion of thestructure at the natural vibration frequency of the structure.

7. A method of prestretching Wire ropes or other structures formed ofassembled wires or strands, including vibrating the structure while itis under prestretching tension by contacting it with an elementoscillated by a powered crank actuator, the rotary speed of the crankactuator being adjusted to vibrate the structure at its inherent ornatural vibration frequency.

8. Apparatus for prestretching wire ropes or other structures formed ofassembled wires or strands, comprising spaced coiling and uncoilingdevices for handling the structure and providing a span of the same,means for controlling these devices to cause tensioning of the structurespanned therebetween and means between these devices for vibrating thestructure spanned and tensioned therebetween.

9. Means for Vibrating a tensioned Wire rope or similar structure,comprising a rotary motor, a crank powered by this motor, an element forengaging the tensioned structure, a connecting rod between the crank andelement and means responsive to the vibration frequency o'f thestructure for varying the speed of said motor.

LEONARD C. PESKIN'.

